298 PRACTICAL ORGANIC with quinine in cinchona bark), is now prepared from aniline. The aniline, in process of oxidation to quinone, appears to pass through the following intermediate stages, xNHo / — ^Oll The aniline is first oxidised to phenylammonium oxide, which changes into phenylhydroxylamine. The latter also under- goes intramolecular change, being converted into /-amino- phenol, which is finally oxidised to quinone (Bambcrger). It may also be obtained "by the,oxidation of para-derivatives of aniline, such as /-phenylenediamine, sulphariilic acid, p. aminophenol, &c. Other amino-compounds and phenols yield corresponding quinones, and it can even be prepared from an amino-compound or phenol, if an alkyl group occupies the para- position, as in the case of mesidine, which loses a methyl group and yields jw-xyloquinone. Quinone is sometimes regarded as a superoxide (Graebe), sometimes as a para-diketonc (Kittig). HC< O O ,CH HC/ II cJ c Superoxide formula. cn r formula. The facts in favour of the first are that quinone, like a peroxide, has a strong oxidising action, that on reduction it yields, not a glycol, but a dihydroxybenzene ; moreover, with PCI.-, instead of a tetra-chloro-derivative, a dichloroben/.cnc is formed. In favour of the ketone structure is the formation of a mono- and di-oxime (Golclschmidt), CO C:N()IT IIC Hc.; ';cn CrNOH JIC iid (MI C:NOir.